During milling of strip-shaped rolling stock the rolling stock is generally fed into the roll stand at a feeding speed which is less than the peripheral speed of the working rolls of the roll stand. As the leading edge of the rolling stock enters the roll gap the roll gap is closed and the rolling stock is milled.
The above method represents the theoretical ideal case, in which the leading edge is aligned in parallel to the roll gap and thus also enters the roll-gap in this alignment. In practice however it can occur that the two ends of the leading edge enter the roll gap after each other, the leading edge thus has an angled position relative to the roll gap. In this case what is referred to as a diagonal delay occurs, which on the one hand leads to an excess width of the rolling stock, on the other hand the rolling stock assumes the shape of a parallelogram. Both effects reduce what is known as yield, meaning the proportion of usable rolling stock volume.
To avoid the angled position, the prior art employed so called material guides. The material guides are adjusted laterally to the strip-shaped rolling stock. They align the strip-shaped rolling stock such that the leading edge is aligned in parallel to the roll gap.
The alignment of the rolling stock is time-consuming and has a negative influence on the productivity of the rolling mill. In addition only a poor alignment is possible, especially when the strip-shaped rolling stock has a large width-to-length ratio. In addition there is the danger, even with correct alignment of the rolling stock, that the rolling stock will twist again between alignment by the material guides and being fed into the roll gap, so that, despite the material guides, an angled position of the leading edge relative to the roll gap occurs. The danger of twisting of the rolling stock is in such case all the greater, the greater than 1 the ratio of width to length of the strip-shaped rolling stock is and the smaller the ratio of length of the strip-shaped rolling stock to distance of the transport rollers of the roll train located on the feeding side of the roll stand.